Spiro[5.5]undeca-1,4,8-trien-3-ones are known compounds that are described in Hatchard, Journal of the American Chemical Society, Vol. 80, pp. 3640-3642 (1958); McClure, Journal of Organic Chemistry, Vol. 27, pp. 2365-2368 (1962); and copending applications Ser. No. 472,196 (Roper I) and Ser. No. 660,859 (Roper II), filed Mar. 4, 1983, and Oct. 15, 1984, in the name of Jerry M. Roper. As taught in Roper I, such spiroketones are of interest as antioxidants and/or as flame retardant, insecticide, or pharmaceutical intermediates; and they can be prepared by reacting a 4-aminomethylphenol with a conjugated diene and an alkyl halide, typically at a temperature in the range of about 50.degree.-200.degree. C., in an inert solvent. Roper II teaches that the reaction can be accomplished without the aid of an alkyl halide.